THE MAXIMUM POTENTIAL OF MEASUREMENT WITH THE ARAMIS NETWORK

What is the quality of rainfall measurement in each point
of the France territory with the ARAMIS network of 24 weather radars ? The
answer to this question is not simple, because the capability of each radar
to measure rainfall varies in time according to the variations of the atmosphere
characteristics, with seasons but also for each rain event, and even for each
rain structure. Also, no constant masks (trees, buildings, electricity pylons)
can reduce the accuracy of each radar measurement. Even with correction treatments,
these phenomena produce variations in the quality of the rainfall measurement.
Some researchers, as Hervé Andrieu (LCPC) et Guy Delrieu (LTHE) in France,
have demonstrated the importance to take into account notions of "Vertical
Profile of Reflectivity" (VPR) and "Hydrologic Visibility" in the radar data
use.

Using these notions, it is possible to simulate with a good
reliability the rainfall measurement of a weather radar, and ALICIME has realised
several important studies in this field for Météo-France, the French Met.
Office (see
here for example). One of the results of these studies is the estimation
of the maximum potential of measurement with the current ARAMIS
network of 24 weather radars. This estimation suppose a complete volumetric
scan of the atmosphere for each radar, by using a great number of radar beam
elevation angles. ALICIME has demonstrated that this maximum can be approached
very closely by only 2 to 4 beam elevation angles, specifically chosen for
each radar.

The picture below is a simplified representation of this
maximum potential of measurement of the current ARAMIS network. TAKE
CARE: This map do not describes the quality
of the radar products actually diffused in France (contact
Météo-France for this). This map only represents the variability of the maximum
capabilities of measurement with the current radar network, and allows to
identify the areas with the best and the lowest "a priori" quality of the
radar data if this maximum is realised. As the treatment of the radar data
to produce final products are not perfects, this map give a representation
of the variation in quality of the radar rainfall estimations in France, with
the best volumetric measurements and the best radar data processing.

§Potential contribution of the other European radars

In order to take into account the capabilities provided
by the European weather radar networks, we have estimated the contribution
to the ARAMIS rainfall measurement of 4 neighbouring radars: the radar of
the Jersey Island (Channel Island close to Normandy), the radar of Wideumont
in Belgium, the radar of Feldberd in Germany, and the radar La Dole in Switzerland.

The picture below present the areas of the French territory
were the measurements of these radars could be interesting, particularly for
the Jersey radar, the La Dole radar, and the Wideumont radar.

It is interesting to note that the Italian radars and the
Spanish radars are not interesting over the French territory, but improve
rainfall measurement over the Mediterranean Sea.